Numerical Modeling and Simulation of Flame Spread Over Charring Materials.

摘要

The overall objective of this dissertation is the development of a modeling and simulation approach for upward flame spread. This objective is broken into two primary tasks: development of a porous media charring model for carbon-epoxy composites and an algorithm to couple flow and structural solvers. The charring model incorporates pyrolysis decomposition, heat and mass transport, individual species tracking and volumetric swelling using a novel finite element algorithm. Favorable comparisons to experimental data of the heat release rate (HRR) and time-to-ignition as well as the final products (mass fractions, volume percentages, porosity, etc.) are shown. The charring model and flow solvers are coupled using a newly developed conjugate heat and mass transfer algorithm designed for complex geometries in fire environments. Highlights of the coupling algorithm include: a level set description of complex moving geometry, perfect conservation of energy and mass transfer across the interface, a no-slip and no-penetration ghost-fluid interface description, and a patch level set update system that balances accuracy and computational efficiency by reducing the resolution of the Lagrangian model away from the interface. A systematic study of grid convergence order and comparison to analytical benchmark problems is conducted to show the soundness of the approach. The interface methodology is combined with the carbon-epoxy charring model and is used to study burning composites. Comparison of simulations to experimental data show good agreement of composite material response and flame spread (critical heat flux).